A knowledge of the molecular events involved in the formation and repair of chromosome aberrations is fundamental to the understanding of a several biological phenomena, including mutation, malignant transformation, loss of cell viability, and birth defects. Until recently, such understanding has been hampered by the absence of sensitive techniques to determine which specific DNA lesions are responsible for the production of chromosome aberrations. The purpose of this proposal is to elucidate the molecular mechanisms of chromosome aberration formation in human cells by the simultaneous monitoring of induction and repair of specific DNA lesions with that of chromosome lesions. With this project we propose to combine the use of premature chromosome condensation (to study chromosome damage), alkaline and neutral DNA elution (to study DNA damage), DNA repair inhibitors, DNA repair deficient human cell lines, and DNA modifying enzymes. Four general interrelated experimental approaches are proposed and include the following: (1) A comparison of DNA and chromosome repair kinetics after treatment of quiescent human fibroblasts with direct-acting clastogens; (2) The effect of DNA repair inhibitors on the formation of chromosome damage and the in vivo manipulation of specific DNA lesions into chromosome damage and the in vivo manipulation of specific DNA lesions into chromosome breaks; (3) The development of systems for studying chromatin modifications during repair; and (4) A determination of the role of the nuclear matrix as a site of DNA repair. The information generated by these studies will have significant implications in several health-related areas, including the molecular action of chemotherapeutic agents, the development of new rationales of combination chemotherapy in the treatment of malignancy, and the long term effects of clastogenic agents on cellular genome integrity. These studies might also result in the development of a very sensitive assay for the detection of carcinogenic lesions in human cells.